Without moving your shoulder at all, bend at the elbows and lower the weight to your forehead or either sides of your head.

Make sure your upper arms are within your body and not flared out to the outside.

Once the weight is at the low point, contract your tricep and bring the weight back to the top starting position.

You can also preform this movement using a straight bar or EZ bar. Same rules apply, make sure not to move at the shoulder joint and keep the elbows in. The bar will go to your forehead or crown of your head.

Tips:

Make sure the upper arm is not moving during the entire movement. If you need to help yourself to not move it, preform exercise one arm at a time using your opposite hand to stabilize your working arm by holding at your upper arm so it doesn't move back and forth during the rep.